[RFC] mipi-i3c-hci: Support for DMA Ring Pipelining / High-throughput Streaming

[Sam Agazaryan]

Hello all,

I am working on a project using the mipi-i3c-hci driver that involves
large packet bursts (exceeding the physical hardware DMA ring size,
such as large MCTP-over-I3C payloads).

I noticed that the current driver implementation treats these as
discrete batches.

I am considering implementing a ring pipelining or DMA streaming
mechanism to allow for asynchronous refills while the ring is running.
This would leverage the
standard ENQ_PTR doorbell mechanism (per MIPI HCI v1.2, Section 6.8.2)
to continuously feed the hardware. I figured in that case it may be
worth while to see how the upstream community feels about this
feature.

Before I dive into the implementation for upstream, I wanted to check:
1. Is there any existing work or a roadmap for DMA
streaming/pipelining in the HCI driver?
2. Is a generic dma streaming mechanism for large transfers something
you would be interested in seeing as a contribution to the mainline
driver?

Currently, my proof-of-concept handles the pipelining at the core
transfer level, but I
suspect for a generic upstream implementation, this sliding window
logic should be moved into dma.c to properly support controllers with
multiple Ring Bundles.

I would appreciate any thoughts on this approach or the preferred
architectural placement.

Best regards,
Sam